1. Field of the Invention
The present invention relates to a measuring cell with a casing for housing a sensor, in particular a pressure transducer. In particular, the present invention relates to a measuring cell with a casing for housing a sensor, in particular a pressure transducer, in which the casing has a pressure compensation vent for the sensor mounting device
2. Description of the Related Art
The related art involves measuring cells, including those known from DE 10 2007 001 445 A1, the entire contents of which are herein incorporated fully by reference.
In metrology it is frequently necessary to operate measuring equipment in potentially explosive environments. To prevent any explosion risk being caused by such measuring units, these are placed into explosion-proof (e.g., “ex-proof”) enclosures, where the type of ignition protection is a flame-proof enclosure design. In case of an explosion, such enclosure must both withstand the pressure occurring on the inside and prevent the explosion from spreading into the explosive atmosphere which surrounds the enclosure.
These enclosures are normally provided with gaps that are resistant to ignition-flashovers to reduce the high gas pressure that is created inside of a pressure-resistant encapsulated enclosure during an explosion. Such gaps, which normally exist in an enclosure, since cable bushings for measuring signal lines to the outside must also be provided, it is unfortunately a fact that the dimensions must be so tight and of a great length so that a flame of an explosion is extinguished and the temperature of the explosion gases is reduced sufficiently by cooling, so that no ignition can occur in the surrounding atmosphere. These construction requirements provide manufacturing difficulties.
The gap size is specified, depending on the gas composition in the potentially explosive atmosphere, pursuant to the European Standard EN 50 018.
It is also known that to separate zones of potentially explosive areas for an enclosure, a contact bushing for measuring signal lines of a sensor located in the housing must be provided with pressure-proof glass seals with glass-covered metal contacts, wherein pursuant to the standard to be applied, a capillary tube with an inside bore of 0.2 mm and a length of 17 mm was used for pressure equalization. This complex construction is substantial disadvantageous, however, because due to the strict requirements for sealing and absence of cracks in the glass joints, this results in high production costs and high production losses.
In DE 198 26 911 A1, the entire contents of which are incorporated herein by reference, there is described a pressure-resistant flameproof encapsulated enclosure, which has gaps that are resistant to the ignition-flashovers and where the gap surfaces are essentially parallel to each other. These gaps are designed with a stream-splitting device that delimits the interior of the enclosure and projects into it, which projects on its side facing away from the gap of the respective enclosure wall, forms a point, and one side of which extends oblique and merges into the enclosure wall. Such structural design of the gap and the enclosure is also to improve the effect of suppressing the propagation of explosions to the extent that the same degree of safety can also be achieved with larger gap widths or reduced gap lengths.
Accordingly, there is a need for an improved measuring cell with a casing for housing a sensor, in particular a pressure transducer.